1. Field of the Invention
The present invention relates to a monolithic inductor used as, for example, an inductor or coil and, more specifically, the present invention relates to a monolithic inductor having a greatly improved connecting structure between coil conductors in a sintered ceramic body.
2. Description of the Related Art
Various monolithic inductors having a coil conductor embedded in magnetic ceramics are known (See for example, Japanese Patent No. 2655657, Japanese Unexamined Patent Application Publication No. 62-189707, Japanese Unexamined Patent Application Publication No. 59-152605).
Such a conventional monolithic inductor is manufactured by printing a conductor pattern on a ceramic green sheet which is composed almost exclusively of magnetic ceramics, laminating a plurality of such ceramic green sheets, and sintering the ceramic green sheets as a unit to obtain a sintered ceramic body, whereby a plurality of conductor patterns printed on a plurality of ceramic green sheets are connected through via-hole electrodes so that a coil is constructed in a sintered ceramic body.
FIGS. 6 to 9 are explanatory schematic plan views of the above described conductor pattern in a conventional monolithic inductor. While there are shown only the coil conductor sections in FIGS. 6 to 9, a coil conductor section is printed on each ceramic green sheet by screen printing or other suitable process.
In a structure shown in FIG. 6, several xc2xe-turn coil conductor sections 51-53 are electrically connected via electrodes 54 and 55. Each coil conductor section 51 to 53 is printed on the respective ceramic green sheet and has a xc2xe-turn. In other words, when viewed from the top, it appears to be a coil having a rectangular shape, however the coil conductor sections 51-53 each constituting a xc2xe-turn of a rectangular coil are printed on the respective ceramic green sheets.
In a structure shown in FIG. 7, the coil conductor sections 56-58 are connected through via-hole electrodes 59 and 60. Each of the coil conductor sections 56-58 constitutes a turn of a rectangular coil.
In a structure shown in FIG. 8, the coil conductor sections 61 and 62 are electrically connected through a via-hole electrode 63. Each of the coil conductor sections 61 and 62 constitutes 2.25 turns of a coil composed of coil conductors.
In a structure shown in FIG. 9, the coil conductor sections 64, 65 are connected through a via-hole electrode 66. Each of the coil conductor sections 64 and 65 constitutes 2.25 turns of a coil composed of coil conductors.
In the coil conductor sections 64 and 65 shown in FIG. 9, by increasing the number of turns of a coil conductor section printed on a green sheet, miniaturization of a monolithic inductor may be realized.
As described above, by increasing the number of turns of each coil conductor section to be printed on each ceramic green sheet, miniaturization of a monolithic inductor may be achieved. However, there is a recognized disadvantage that if a coil conductor section of more than one turn is formed on a ceramic green sheet as in the structures shown in FIGS. 7 to 9, even if the number of turns is increased, a large inductance corresponding to the increased turns cannot be obtained. This will be explained referring to FIG. 10 and FIG. 11.
FIG. 10A is a cross-sectional view illustrating a portion of a monolithic inductor having coil conductor sections 56-58 of FIG. 7 taken along the line Axe2x80x94A in FIG. 7. In the monolithic inductor 71, upper and lower coil conductor sections, that is, the coil conductor section 56 and the coil inductor section 57, for example, are arranged in such a manner that the upper and lower coil conductor sections 56 and 57 overlap one on another in the direction of thickness via a ceramic layer on the side opposed to the side where the via-hole electrodes are provided. However, in the vicinity of the portion where the via-hole 59 is provided, in other words, in the vicinity of the extremity 56a of the coil conductor section 56 and the extremity 57a of the coil conductor section 57, as will be apparent from FIG. 10A and FIG. 7, the upper and lower coil conductor sections 56 and 57 do not overlap one another in the direction of thickness.
Likewise, FIG. 10B is a cross-sectional view illustrating a monolithic inductor having coil conductor sections 61 and 62 of FIG. 8 taken along the line Bxe2x80x94B of FIG. 8. In this case as well, in the vicinity of the extremity 61a of the coil conductor section 61 and in the vicinity of the extremity 62a of the coil conductor section 62, the upper and lower coil conductor sections 61 and 62 do not overlap one another in the direction of thickness and are not aligned.
FIGS. 11A and 11B are cross-sectional views illustrating the monolithic inductor using the coil conductor sections 64 and 65 of FIG. 9 taken along the lines Cxe2x80x94C and Dxe2x80x94D of FIG. 9 respectively. When the coil conductor sections 64 and 65 of 2.25 turns are laminated alternately, non-alignment portions between the upper and lower coil conductor sections 64 and 65 are present in the vicinity of the extremity 64a of the coil conductor section 64 and in the vicinity of the beginning end 65a of the coil conductor section 65.
In other words, while the upper and lower coil conductor sections 51-53 can be overlapped precisely on one another in the case of coil conductor sections 51 to 53 of xc2xe-turn shown in FIG. 6, there is a portion where the upper and lower coil conductor do not align in the direction of thickness when the number of turns is increased. When the portion where the upper and lower coil conductor sections are not aligned via the ceramic layer in the direction of thickness is formed, the magnetic path in that portion is hindered, thus lowering the efficiency of inductance which is obtained by the inductor component. Since the coil conductor sections shown in FIG. 6 are xc2xe-turn sections, when these coil conductor sections are laminated, the distances between the coil conductor sections in the direction of lamination becomes wider in some portions. As a result, deterioration of the characteristics associated with the leakage of magnetic flux occurs.
In order to overcome the problems described above, preferred embodiments of the present invention provide a monolithic inductor wherein the formation of portions where the upper and lower coil conductor sections do not overlap on one another is reduced even when the number of turns of a coil conductor section provided on a ceramic green sheet is selected to be 1 or more to achieve miniaturization, and thereby a large inductance is obtained.
According to one preferred embodiment of the present invention, a monolithic inductor includes a sintered ceramic body, and a plurality of coil conductor sections in which each coil conductor is wound by at least one turn, wherein the plurality of the coil conductor sections are located at vertical positions in the sintered ceramic body, and the upper and lower conductor sections are electrically connected through via-hole electrodes to define a coil, a terminal end of the upper coil conductor section and a beginning end of the lower coil conductor section are bent inwardly from the innermost portion of the coil such that a connecting portion of the coil where the upper and lower coil conductor sections are electrically connected through a via-hole electrode is located within the innermost portion of the coil defined by the upper and lower coil conductor sections.
According to at least one preferred embodiment of the present invention, a coil is preferably a substantially rectangular coil in a plan view, and the terminal end of the upper coil conductor section and the beginning end of the lower coil conductor sections are respectively bent in a direction that is substantially perpendicular to the innermost substantially rectangular coil portion.
According to another preferred embodiment of the present invention, in the outer connecting portion of the coil where the upper and lower coil conductor sections are electrically connected, a terminal end of another upper coil conductor section and a beginning end of another lower coil conductor section are electrically connected through a via-hole electrode in the outermost portion of the coil.
According to further preferred embodiment of the present invention, the sintered ceramic is an integrally sintered ceramic body which is formed preferably by laminating and sintering a plurality of ceramic green sheets each having a coil conductor section of at least one turn printed thereon.
Other characteristics, features, elements and advantages of the present invention will become apparent from the following detailed description of the preferred embodiments thereof with reference to the attached drawings.